The invention is related to an actuator, comprising a housing, a motor, an actuating member and a screw mechanism providing a linear movement of the actuating member with respect to the housing in response to a rotational movement of the motor, which screw mechanism comprises a screw and a nut one of which is rotatably supported with respect to the housing by means of an angular bearing, and a reduction gear means.
Such actuator is known from WO-A-9603301. Said known actuator, which is a part of an electrically actuatable brake calliper for a disc brake, comprises a roller screw mechanism and a satellite gear wheel mechanism. The screw mechanism is accommodated partly within an electric motor. The end of said screw mechanism which protrudes from the electric motor towards the brake pads, carries an integrated thrust bearing as well as an integrated satellite gear wheel mechanism.
The satellite gear wheel system is positioned around the screw mechanism. This position leads to rather big radial dimensions of the satellite gear wheel system, whereby the stiffness of said system is reduced and the operational deflections are increased. Thus, the required transmission stiffness cannot be maintained. Moreover, as a result of this layout, this known actuator is rather complicated and therefore rather cumbersome with respect to manufacturing.
A further drawback of the complicated integrated structure of the prior art actuator is related to the area of manufacturing. Usually, manufacturing of rolling mechanisms such as the rolling bearing and the screw mechanism require a different background than manufacturing gear systems. As these components are integrated to a considerable degree in the prior art actuator, problems may arise as to the proper selection of combined required different manufacturing technologies and the proper control of these manufacturing processes.
The object of the invention is therefore to provide an actuator which does not have these disadvantages. This object is achieved in that the actuating member and the reduction gear means are situated at opposite ends of the screw mechanism.
In the actuator according to the invention, the reduction gear means is at a different position than the screw mechanism, which has several advantages. For instance, such position is less subject to space constraints. Furthermore, the reduction gear means is at a distance from the actuating member, which allows more space and freedom of design for those components.
According to a further important advantage of the invention, the actuator can now be carried out in such a way that the reduction gear means is contained in a reduction gear module and the screw mechanism is contained in a screw mechanism module, said reduction gear module and screw mechanism module being interconnected through a drive module.
The modular layout of the several components which make up the drive line of the actuator, enables the application of dedicated required manufacturing technologies and processes for each individual component of the entire system. Also, the modular design opens ways for parallel production of components, leading to a more streamlined and cost effective production process.
Nevertheless, after manufacturing the said components in this way, they may be united in pre-assembled sub-units. For instance, the reduction gear module and the screw mechanism module are integrated, or the screw mechanism module and the drive module are integrated.
The layout of the several modules may be designed such that at least two modules are axially aligned, or that at least two modules are axially shifted or excentric with respect to each other.
According to a preferred embodiment, the drive module is situated between the reduction gear module and the screw mechanism module.
A drive system with an electric drive module may have a first drive shaft engaging the electric motor and the reduction gear module, and a second drive shaft interconnecting the reduction gear module and the screw mechanism module, wherein the first and the second drive shaft are coaxial and are mutually supported by means of at least one rolling element bearing.
Advantageously, the first and second drive shaft are accommodated within each other, the rotor of the electric motor engaging the outer drive shaft.
In order to better accommodate the loadings on the actuating member, the screw mechanism module may comprise an angular contact bearing.
Said bearing may be supported within the housing in different ways. According to a first possibility, the outer ring of the angular contact bearing rests against the radial surface of the inwardly protruding flange facing away from the brake pads, said outer ring and flange being held against each other by means of bolts under tension.
According to a second possibility, the outer ring of the angular contact bearing rests against a radial surface of the inwardly protruding flange which faces towards the brake pads. In this embodiment, the outer ring is pressed firmly onto said flange under the influence of the actuating forces, which means that such construction can do without highly loaded bolts.
The reduction gear module may comprise at least part of a planetary gear system having a stationary outer ring gear with inwardly pointing gear teeth. In particular, the reduction gear module may comprise satellite gear wheels which mesh with the ring gear and which are accommodated on a carrier connected to a rotary shaft engaging the screw mechanism, and the sunwheel of the planetary gear system may be accommodated on a drive shaft of the drive module.
Alternatively, the nut may engage the stationary ring of the angular contact bearing by means of a holding member, such that the nut is slidable in axial direction but non-rotatable, and the screw is supported rotatably but non-slidable by means of the rollers and a bearing.
Furthermore, a sensor may be provided for detecting rotational and/or translational movements of the screw mechanism. Also, control means may be provided, said control means having an input for a control signal, e.g. from a brake pedal, and being connected to the sensor fear controlling the electric motor on the basis of the control signal and the signal from the sensor. The sensor is in particular suitable for obtaining force feedback, wear compensation and/or maintenance indication.
The actuator according to the invention can be applied for different purposes. In particular, the actuator is suitable for use in a brake calliper for an electrically actuatable disc brake, said calliper comprising an actuator as described before, and a claw piece carrying two opposite brake pads, said actuator comprising a screw and a nut one of which is rotatably supported with respect to the housing by means of an angular bearing, and a reduction gear means.